Imine-Linked Porous Organic Polymer Gel and Immobilization of Copper(II): Easy Synthesis and Excellent Catalyst for Huisgen [3+2] Cycloaddition Reactions

Porous organic polymeric gels (POP gels) were made by condensation of a newly synthesized C-3-symmetrical azobenzene-based tri-salicylaldehyde building block, 1,3,5-tris(4-((3-formyl-4-hydroxyphenyl)diazenyl)phenyl)benzene (TAzo) with suitable aromatic tri- and di-amines in N,N-dimethylformamide (DMF) at ambient conditions. Here, we have furnished the pathway of an efficient, gentle, and simple one-pot synthesis of imine-linked porous organic polymers at room temperature without any acid catalysts. Detail rheological properties of the POP-gels were studied and were also found to be stable for at least a year at room temperature. Nitrogen isotherm revealed the mesoporous nature of the gel-powders with moderate surface area. Iminophenol moieties are known to provide binding sites to metallic species via the strong coordination interaction with hydroxy (-OH) and imine (-HC=N-) groups. We have successfully synthesized a copper-metallated POP by immobilizing copper ions in one of the POP-gels. The mesoporous POP material having 3 wt % copper loading was utilized for the solvent-free Huisgen [3+2] cycloaddition reactions of various aryl, benzyl, and alkyl azides with terminal alkynes containing aromatic, heteroaromatic, and alkyl groups with excellent yield. The heterogeneous catalyst with low catalyst loading (1 mol %) was highly regioselective towards 1,4-disubstituted 1,2,3-triazoles, recyclable, and did not require the addition of a reducing agent.